By "maximally tolerated" pentobarbital dosing, daily for five weeks, we have developed a quantitatively defined and reproducible barbiturate dependency cat model to use as a control. 1. Against this reference, effects of low chronic dose, and of frequency and duration of exposure to barbiturates will be investigated in relation to (a) tolerance characteristics, and (b) withdrawal sign intensities. 2. The cat model system will provide the basis for a meaningful evaluation of withdrawal treatments. The effective uses of the benzodiazepines (diazepam and chlordiazepoxide) will be compared to that of the established phenobarbital treatment. 3. Pharmacokinetics of benzodiazepines will be defined for their parent drugs and active metabolites to provide the rationale for a chronic dosing regimen for future study. 4. Neurophysiologic alterations during withdrawal will be examined; their neuronal loci and mechanisms will be further investigated utilizing extra- and intracellular microelectrode recording techniques in spinal segmental reflex pathways. 5. After establishing low-level pentobarbital dependency, the sleep study will be continued. The effects of low-level chronic dosing will be compared with those produced by "maximally tolerable" dosing.